Bar (unit)

The bar is a unit used to measure pressure. It is not part of the main system of units used by scientists, but it is still very useful. One bar is almost the same as the pressure we feel from the air around us at sea level—it is just a little bit less.

This unit was created by a Norwegian scientist named Vilhelm Bjerknes, who helped start modern weather forecasting. He defined one bar as a certain amount of force on a small area.

Even though the bar is not part of the main system, it is allowed to be used in some places, like in weather reports in Europe. Scientists in other areas usually prefer different units, but they sometimes use the bar when talking about weather and space. There are also smaller and larger versions of the bar, like the millibar and the megabar, to help describe different pressures.

Definition and conversion

The bar is a way to measure pressure. It is defined as 100,000 pascals, which is a unit used in science.

One bar is about the same as the pressure we feel from the air around us at sea level. It can also be changed into other units like atmospheres, pounds per square inch, inches of mercury, millimeters of mercury, Torr, and centimeters of water. A smaller unit called a millibar is just one-thousandth of a bar.

Origin

The word bar comes from an Ancient Greek word baros, which means weight. This unit of pressure uses the symbol bar. An older symbol, b, is no longer recommended because it can be confused with other units, but you might still see it used, especially as mb for millibar. Long ago, between 1793 and 1795, the word bar was also used for a unit of mass, similar to what we now call a tonne.

Usage

Air pressure is often measured using a unit called the millibar. Even though it is not part of the main system of measurement units, weather experts all over the world use millibars because the numbers are easy to work with. Some places now use hectopascals instead, which are the same as millibars. For example, weather maps in Canada show pressure using kilopascals and hectopascals.

In diving, the bar is commonly used to show how much pressure there is underwater. A full scuba tank holds about 200 bars of air, and every 10 meters of seawater adds about 1 bar of pressure.

Engineers like using bars because it avoids very large numbers when talking about pressure. In cars, tire pressure and turbocharger boost are often given in bars. In machines that use fluid pressure, such as hydraulic systems, pressures can be in the hundreds of bars.

In ships, pressures in systems like cooling water are also measured in bars.